Historic Dispute : Is Earth the center of the universe?

Viewpoint:
Yes, early scientists believed that what appeared to be movement around
Earth by the Sun and other entities was, in fact, just that.

Viewpoint:
No, later scientists such as Nicolaus Copernicus and Galileo correctly
realized that Earth moves around the Sun, not vice versa, and thus cannot
be the center of the universe.

It is easy in our human nature to believe that we are the center of the
universe. A newborn infant must learn through experimentation and
sensation that he is a part of the world, not the entirety. Any parent can
attest that as children mature, they must be helped to understand that the
universe does not revolve around them and their needs and desires. Even as
adults, we often struggle to see the world from a perspective other than
our own.

Likewise, it was natural for ancient peoples to assume that the universe
they observed was centered upon Earth. After all, they saw the Sun rise in
the east every morning, and set in the west at night. They saw the stars
and planets appearing to move across the sky. These patterns were repeated
in cycles, and cycles implied revolution. There was no reason to question
that what appeared to be movement around Earth was, in fact, just that. By
the fourth century
B.C.
, the Greeks had developed a picture of the stars as fixed on a celestial
sphere that rotated around Earth, with the Sun, Moon, and planets moving
independently beneath it.

In accordance with Greek philosophy, the orbits of the heavenly bodies
were assumed to be a circle, regarded as a "perfect shape."
As astronomers carefully recorded the apparent movements of the stars and
planets, this conceptual model needed to be adjusted to account for the
observations. The planets, named from the Greek word for
"wanderers," were a particular problem, because sometimes
they appeared to move backward. In the second century A.D., Ptolemy
developed a complex system of circles within circles, called epicycles,
which accurately reproduced the observed celestial patterns.

In the sixteenth century, the Polish scholar Nicolaus Copernicus proposed
that the Sun was the stationary center of the universe, with Earth,
planets, and stars moving around it. However, Ptolemy's model was
more accurate in predicting the celestial movements, since that was what
it had been designed to do, and this provided a powerful argument against
the Copernican system. Another competing model was that of the Danish
astronomer Tycho Brahe. The Tychonic system held that the Sun and Moon
revolved around Earth, while everything else revolved around the Sun.

When the seventeenth-century Italian scientist Galileo Galilei built his
telescope, he observed that the planet Venus showed phases, and deduced
that it orbited the Sun. He also found four moons orbiting the planet
Jupiter, conclusively disproving the idea that everything in the universe
revolved around Earth. Although these observations were consistent with
either the Copernican or Tychonic model, Galileo threw his lot in with
Copernicus.

Nicolaus Copernicus
(
Copernicus, Nicholas, engraving
.

The Library of Congress.

)

Likewise, Tycho Brahe's assistant, Johannes Kepler, became an
adherent of the Copernican model. After his mentor's death, and
using Tycho's extensive and precise observations, Kepler developed
a heliocentric system in which the orbits were elliptical rather than
circular. This finally produced more accurate predictions than
Ptolemy's epicycles and greatly advanced the Sun-centered
(heliocentric) view.

The concept of ourselves as the center of the universe was no easier for
human societies to give up than it is for individuals. Copernicus escaped
censure because his theories weren't published until he was on his
deathbed. Galileo, however, attracted the attention of the Inquisition,
and was found guilty of heresy, forbidden to publish, and sentenced to
house arrest for life. This was relatively lenient treatment for the time,
perhaps meted out because of Galileo's age and poor health. In
1600, the philosopher Giordano Bruno had been burned at the stake for
espousing the same ideas.

Moving the designated center of the universe from Earth to the Sun may
have been the hardest step, but it was only the beginning. As astronomy
progressed in the nineteenth and early twentieth centuries, we gradually
became aware that our planet orbits an ordinary star tucked away in an arm
of an ordinary spiral galaxy, of no particular prominence within an
enormous universe. But most people don't find that discouraging.
Though it turns out that we are not at the center of anything, the
universe we know today has far more wonders than Ptolemy could have
imagined.

—SHERRI CHASIN CALVO

Viewpoint: Yes, early scientists believed that what appeared to be
movement around Earth by the Sun and other entities was, in fact, just
that.

Throughout most of recorded history, man believed that Earth was the
center of the universe. This belief, which we now call the geocentric
theory of the universe, was so strong that the few who dared to
challenge it were often persecuted or even killed for their heretical
beliefs. The persecution suffered by Italian mathematician and
astronomer Galileo Galilei during the early seventeenth century for
expressing his views opposing the prevailing geocentric model is well
known. On the other hand, few are familiar with the story of Italian
philosopher Giordano Bruno. Bruno was burned as a heretic in 1600 for
supporting the same position as Galileo, namely that the Sun was
actually the center of the universe and Earth revolved around it while
rotating on its own axis. For centuries it had been an integral part of
man's belief system that Earth was the center of the universe.
This belief was not easily overturned.

There were many reasons for man's conviction that a geocentric
system described his universe. Mythology and religion played important
roles, as did prevailing scientific theories. However, probably the
oldest and most persuasive reason for believing that Earth was the
center of the universe was common sense based on everyday observations.

The Geocentric Theory

For an untold number of years, man had watched the Sun
"rise" in the east every morning, move across the sky
through the day, and "set" in the west. This simple motion
repeated itself the next day, and the next, and the next, ad infinitum.
Man had no reason to suspect that this daily motion was anything other
than what it seemed, or that it had ever been different, or would ever
change. Some explanations for this phenomenon were based on myths. For
instance, one such myth envisioned the Sun dying every day only to be
reborn the next day. However, the obvious logical explanation for the
Sun's movement was that Earth is a stationary object, and the Sun
revolved about it every day. It is comparable to
looking out a window at a scene as it passes by one's field of
vision. You may be moving past the stationary scenery, or you might be
stationary while the scenery moves past your window. If you experienced
no sensation of movement, the obvious conclusion would be the latter.
Man experienced no sensation of movement on Earth; therefore, the
conclusion was that the Sun moves while Earth remains stationary.
Because similar observations were made of the motion of the Moon and the
planets (although their motion was a bit more complicated), it was
thought that Earth must be at the center of the universe. Then the
heavenly bodies revolved about Earth. There was very little reason to
suspect otherwise.

The ancient Babylonians observed and studied the motions of the heavens,
even developing mathematical techniques to predict the motions of the
heavenly bodies. However, it was the Greeks who first developed
scientific theories concerning these motions. With only a few
exceptions, the ancient Greek philosophers believed Earth was the center
of the universe. One Greek philosopher, Eudoxus, proposed a rather
complicated system of fixed spheres to which the Sun, Moon, the five
known planets (Mercury, Venus, Mars, Jupiter, Saturn), and the stars
were attached. With Earth fixed at the center, these spheres revolved
and carried the heavenly bodies in a circular motion around Earth. By
employing some rather sophisticated mathematics, Eudoxus was able to
explain reasonably well the motion of the Sun and Moon, as well as the
motions of the planets. However, his system was only partially
successful in predicting the motion and location of the various heavenly
bodies as they revolved about Earth. One reason for the popularity of
Eudoxus' model was that it was adopted by Aristotle. Aristotle
was a Greek philosopher whose teachings were extremely influential until
the dawn of modern science.

Greek astronomers realized that observational discrepancies existed in
the geocentric theory of the universe. The most obvious difficulty was
the unexplained irregularities in the motion of the planets. Astronomers
noted that the planets sometimes appeared to move in a direction
opposite to that of their usual movement. This motion, called retrograde
motion, presented a mathematical and physical puzzle that was tackled by
many Greek astronomers. They constructed ingenious models that met with
varying degrees of success to explain retrograde motion. Eudoxus'
model of the universe, with its collection of concentric spheres, was
useful in explaining retrograde motion for some, but not all, of the
planets.

The puzzle of retrograde motion, as well as certain other incongruencies
in Eudoxus' system, was eventually "solved" by the
use of

Figure 1
(

Electronic Illustrators Group.

)

Figure 2
(

Electronic Illustrators Group.

)

epicycles. Essentially, an epicycle is a circle on a circle. The planet
moves on a circle (called the epicycle) while this circle revolves
around Earth on a larger circle (see figure 1). In this way, the planet
appears to move backwards on occasion as it moves around its epicycle in
the direction opposite to its motion on the larger circle. The use of
epicycles helped preserve two of the primary tenets of ancient
astronomy: the centrality of Earth and the belief in the perfection of
uniform circular motion in the heavens.

The Ptolemaic Model

The work of the second-century Greek astronomer Ptolemy represents the
apex of the geocentric theory. In his work, entitled the
Almagest
, Ptolemy described a complicated system that was exceptionally
accurate in its description of the motion of heavenly bodies. To do so,
Ptolemy had to expand on Aristotle's rather simplistic
description of circular motion. Ptolemy used two devices in his model in
an effort to predict more accurately planetary motion: the previously
mentioned epicycle and another device called eccentric motion. Eccentric
motion was one in which the planet traveled around a circle whose center
was not Earth (see figure 2). Although both epicyclical and eccentric
motion had been proposed by Apollonius as
early as the third century
B.C.
, it was Ptolemy who eventually used these two devices to construct a
geocentric model that was successful in matching observational data.
This system had the added benefit of providing an explanation for the
varying length of the seasons, a feat earlier models had failed to
accomplish.

The Ptolemaic model proved successful in predicting the motions of
heavenly bodies and was the prevailing theory used by astronomers for
centuries. However, the Ptolemaic model was not universally accepted.
The eccentric motion violated the basic premise of uniform circular
motion as prescribed by Aristotle. There were those, like the
eleventh-century Muslim scientist Ibn al-Haytham, who tried to create
models retaining the predictive powers of the Ptolemaic system without
sacrificing the doctrine of uniform circular motion. Ultimately
Ptolemy's model won the day, primarily due to its impressive
accuracy.

Aristotelian Physics

In addition to everyday observations, another argument for the
centrality of Earth evolved from the physical theories of Greek
philosophers, especially Aristotle. Aristotelian physics, which was the
dominant paradigm until the Scientific Revolution, assumed the existence
of five elements. Four of these elements, earth, water, air, and fire,
formed the world and its surrounding atmosphere. The fifth element, the
ether, was perfect and unchanging and formed the celestial bodies. In
Aristotle's conception of the physical world, earth, as the
heaviest element, naturally tended toward the center of the universe. Of
course, this center of the universe was the center of Earth itself.
Water, lighter than earth, also tended toward the center, gathering on
top of the heavier earth. The lighter elements, fire and air, rose and
collected above earth and water. Because the tenets of Aristotelian
physics became so ingrained into society's picture of the
universe, the concept of the centrality of Earth went essentially
unchallenged. Astronomy began with this belief as a central assumption,
and it was seldom questioned.

Later, in Europe, Aristotelian physics blended with Medieval
Christianity to form a conception of the physical world that would
dominate scientific thought until the work of Galileo, Sir Isaac Newton,
and the other founders of modern science. Ideas such as the perfection
of the heavens, the immobility of Earth, and the centrality of human
creation all contributed to the pervading thought that Earth must be the
center of the universe. The third century
B.C.
Greek mathematician/astronomer Aristarchus was labeled impious for
placing the Sun at the center of the universe. Centuries later,
Christians called upon the Bible to support their geocentric claim. They
argued that Joshua commanded the Sun to stand still during a great
battle so that his army might have more daylight in which to fight
(Joshua 10: 12-13). The key to this passage was that Joshua did not
command Earth to stand still, but rather the Sun. For the Sun to stand
still implied that it must first be moving.

Allusions to ancient philosophers and to the Bible demonstrate that part
of the reason for the acceptance of the geocentric model for so many
centuries was man's preoccupation with authority. Whereas the
Church was the ultimate authority in religious matters, Aristotle,
Ptolemy, and other Greek thinkers were often considered the ultimate
authority on scientific subjects. With a few adjustments made to their
teachings to allow them to coexist with Christian doctrine, the science
and philosophy of the Greeks was accepted almost without question.

The Heliocentric Theory

Although the geocentric model of the universe dominated thought from
ancient time through the seventeenth century, there were those who
proposed the possibility of a Sun-centered, or heliocentric model. This
model, with its requirement that Earth not only revolve about the Sun
but also rotate on its own axis, was fraught with error, according to
common opinion. First, argued the defenders of the geocentric model, if
Earth moved man would have some sort of perception of that movement. If
Earth were moving at the speed required to explain movements observed in
the heavens, a strong wind would continually

Figure 3
(

Electronic illustrators Group.

)

Figure 4
(

Electronic Illustrators Group.

)

blow in the direction opposite to the motion of Earth. In addition, if
one were to throw a stone straight up into the air, a moving Earth would
cause the stone to fall some distance behind its original position.
Everyday observations confirmed that none of these things happened. This
was evidence in support of the geocentric model. Furthermore, it was
ridiculous to assume, the argument went, that the heaviest element
(earth) was propelled through the universe while the lightest (ether)
remained motionless. The precepts of Aristotelian physics made such
motion impossible. It was infinitely more logical that the heavy Earth
was stationary while the light ether possessed the movement necessary to
explain observable phenomena.

An even more sophisticated argument held that if Earth were revolving
about the Sun, the motion of Earth should cause an apparent change in
the position of the stars. This motion is called stellar parallax (see
figure 3). Stellar parallax is not observable to the naked eye, or even
through the first telescopes; therefore, proponents of the geocentric
model argued that Earth was not moving around the Sun. Furthermore, if
stellar parallax could not be observed due to the great distances
involved, the universe would have to be much larger than anyone had
imagined—too large, the geocentric theorists believed, to be a
viable alternative.

Even some time after sixteenth-century astronomer Copernicus proposed
his heliocentric model of the universe, most Europeans clung to the
geocentric model. In answer to some of the questions raised by
Copernicus' model, the Danish astronomer Tycho Brahe developed a
new structure for the universe that was a compromise between the
heliocentric model and the geocentric model. Brahe placed Earth at the
center of the universe, with the Sun and the Moon revolving about it.
However, instead of also requiring the other planets to revolve around
Earth, in Brahe's model the planets revolved about the Sun as it
revolved about Earth (see figure 4). This system seemed to encompass the
physical and theological advantages of the geocentric model, as well as
the observational and mathematical advantages of the heliocentric model.
Brahe's complicated and rather illogical system serves to show
just how far man would go in order to preserve the idea of
geocentricity.

Eventually, all of the arguments used to defend the geocentric model of
the universe were abandoned. The time it took to repudiate these
arguments is a testament to the physical and astronomical systems
devised to explain the world by the Greeks. It would take the complete
overthrow of Aristotelian physics and Ptolemaic astronomy to finally
nullify the geocentric theory. Yet, even today, we speak of the Sun
"rising" and "setting" as if it moved rather
than Earth.

—TODD TIMMONS

Viewpoint: No, later scientists such as Nicolaus Copernicus and Galileo
correctly realized that Earth moves around the Sun, not vice versa, and
thus cannot be the center of the universe.

The geocentric (Earth-centered) model of the universe was almost
universally accepted until the work of astronomers Nicolaus Copernicus,
Galileo Galilei, and Johannes Kepler in the sixteenth and seventeenth
centuries. There were, however, a few radicals who proposed alternatives
to the geocentric model in ancient times. For instance, followers of the
Greek philosopher Pythagoras (to whose school the Pythagorean theorem is
attributed) proposed that Earth revolved around a "central
fire." Although this central fire was not the Sun,
Pythagoras' theory was one of the earliest expressions of the
novel idea that Earth might not be the center of the universe. Later, a
few other Greek philosophers followed suit. In the fourth century
B.C.
, Heracleides sought to resolve difficulties involved in the
observations of Venus and Mercury by proposing that these two planets
revolved around the Sun, while the Sun in turn revolved around Earth.
Heracleides also suggested that Earth rotates. A little later,
Aristarchus of Samos (third century
B.C.
) maintained that the Sun was the center of the entire universe and that
Earth revolved around it. None of these theories, however, exhibited any
marked influence on mainstream scientific thought. In spite of these
heliocentric (Sun-centered) theories, the geocentric model reigned
supreme thanks primarily to the philosophy and physics of Aristotle and
the astronomical work of Ptolemy. It was not until the work of
Copernicus many centuries later that a heliocentric model was seriously
considered.

The Revolutionary Ideas of Copernicus

Nicolaus Copernicus (1473-1543) developed a heliocentric model of the
universe and in the process initiated the Scientific Revolution. In his
model, Copernicus maintained that Earth was not the center of the
universe. Instead, Copernicus believed that Earth and the other planets
revolved around the Sun. Although the notion that Earth was not the
center of the universe presented many problems to sixteenth-century
scientists and theologians, some of the advantages of the Copernican
system over the Ptolemaic were readily apparent. Copernicus'
system offered a simple explanation for many of the observed phenomena
that could not be easily explained within the old system. Retrograde
motion was one such phenomenon. Retrograde motion is the apparent change
in direction that is observed in a planet's motion as it travels
across the sky. The Ptolemaic system attempted to account for retrograde
motion with epicycles. An epicycle is essentially a circle on a circle.
According to the Ptolemaic system the planet moves on a circle (called
the epicycle) while this circle revolves around Earth on a larger
circle. With the Sun at the center of the universe, however, retrograde
motion is easily explained. The apparent change in direction of the
planet is a direct result of its orbit around the Sun (see figure A).
Notice

Figure A
(

Electronic Illustrators Group.

)

the position of the planet (Mercury, in this case) in relation to the
fixed stars. Mercury appears to move in one direction from position 1 to
2 to 3 and then change direction as it moves to position 4. This
movement was much more difficult to explain in the geocentric system of
Ptolemy.

Another advantage of the Copernican system was its ability to simply and
effectively pinpoint the relative position of the orbits of Mercury and
Venus. In the old geocentric models it was never clear in which order
the orbits of Mercury and Venus occurred. When the orbits of these inner
planets were analyzed in the context of Copernicus' heliocentric
model, their positions were, for the first time, unambiguous. The
observations confirmed that the orbit of Venus was closer to Earth than
that of Mercury.

The Advances of Brahe and Kepler

Although revolutionary in his ideas concerning the motions of the
heavenly bodies, Copernicus remained a product of the medieval
Aristotelian natural philosophy. In some ways, Copernicus'
system, as explained in his famous work of 1543,
De Revolutionibus orbium coelestium
(On the revolutions of the heavenly spheres), was similar to the
centuries-old model developed by Ptolemy. For instance, although
Copernicus placed the Sun at the center of the universe, he retained the
notion that the heavenly bodies were carried around on their revolutions
by solid crystalline spheres. It was not until the work of two
astronomers of the next generation, Tycho Brahe (1546-1601) and Johannes
Kepler (1571-1630), that this theory was challenged. Brahe observed two
occurrences in the heavens that cast serious doubt on the theory of
crystalline spheres. First, he observed the birth, and later
disappearance, of a new star (a nova). When Brahe was able to show that
this new object in the sky came into existence beyond the orbit of the
Moon, he challenged the belief that the heavens were perfect and
unchanging. Secondly, Brahe calculated the path of a comet (a hazy
gaseous cloud with a bright nucleus) and showed that it was moving
across the heavens beyond the orbit of the Moon. In other words, its
orbit would take the comet "crashing" through the
crystalline spheres, an obvious impossibility. Brahe concluded that
there were no physical spheres containing the orbits of the planets.

Kepler's contribution to the mounting evidence pointing toward
the truth of Copernicus' theory came in the form of his three
laws of

Galileo
(
Galilei, Galileo, drawing
.

Archive Photos, Inc.

Reproduced by permission
.)

planetary motion. Kepler's first law states that the planets
orbit the Sun following an elliptical path with the Sun at one focus of
the ellipse. This revolutionary break with the tradition of circular
motion allowed a simple geometrical model to explain the motions of the
planets. No longer requiring awkward epicycles and eccentrics,
elliptical orbits presented an elegant mathematical solution to a sticky
problem. Kepler's other two laws are mathematical theories
relating to the heliocentric model. His second law states that the
orbits of planets sweep out equal areas in equal times, and his third
law concludes that the square of the period of each orbit is
proportional to the cube of the semimajor axis of the elliptical
orbit—that is, one half the distance across the ellipsis at its
widest point. The regularity that these three laws implied made the
heliocentric model compelling to scientists who looked for order in the
universe.

Interestingly, we remember Kepler's three laws of planetary
motion but seldom hear of his other theories that did not stand the test
of time. In Kepler's early work,
Mysterium Cosmographicum
(Cosmographic mystery), the astronomer defended the truth of
Copernicus' heliocentric model by constructing his own model in
which the orbits of the planets were separated by the five regular
solids. A regular solid is one whose faces are all identical. For
instance, a cube is a regular solid because its sides are all equal
squares. Since only five such solids exist (cube, tetrahedron,
dodecahedron, icosahedron, and octahedron), Kepler believed it was
God's intention that they appear between the orbits of the six
planets. Kepler argued that this was further proof of the heliocentric
theory because, in the geocentric theory, the Moon was the seventh
planet. If there are only five regular solids, they could not fit in
between the orbits of seven planets. To Kepler, this was important
evidence in favor of accepting the heliocentric model as God's
divine plan.

The Discoveries of Galileo

In one of the most important series of events in the Scientific
Revolution, the Italian scientist Galileo Galilei (1564-1642) turned his
newly acquired telescope toward the sky and discovered many wonders that
would cause man to rethink his previous conceptions of the cosmos. One
of Galileo's first discoveries was that the Moon had surface
features such as craters. This discovery was in direct conflict with the
Aristotelian view of heavenly bodies composed of a perfect and
unchanging substance. The features of the Moon indicated that it might
be composed of the same sort of common material as Earth.

Galileo also discovered, with the help of his telescope, that Venus went
through observable phases just as the Moon. In the Ptolemaic system, the
phases of Venus (undetectable without a telescope) would be impossible.
If Venus orbited Earth, inside of the Sun's orbit, it would never
be seen as full. The fact that Venus appeared in phases was a strong
argument that it was revolving around the Sun.

Two discoveries made by Galileo with the help of his telescope changed
the way man perceived the stars themselves. Galileo noticed that the
planets appeared as solid discs with a well-defined outline when viewed
through the telescope. The stars, on the other hand, continued to
twinkle and resisted definition even when gazed upon through the
telescope. Galileo concluded that the distance to the stars must be many
times greater than the distance to the planets. This meant that the size
of the universe was much greater than allowed by the Ptolemaic model. In
addition, Galileo was able to observe that the Milky Way was actually
composed of many individual stars, suggesting that the number of stars
in the sky was much greater than had been previously believed.

Finally, a crucial discovery made by Galileo was the existence of the
moons of Jupiter. The old paradigm maintained that Earth was the center
of all revolving bodies. This centrality formed the very essence of
Aristotelian physics and Ptolemaic astronomy. The existence of bodies
revolving around a center other than Earth brought into question all of
the previous assumptions upon which science was based. If
Earth was not the center of revolution for all heavenly bodies, then
other tenets of ancient science might also be false.

In addition to the evidence for the heliocentric model discovered by
Galileo with the aid of his telescope, the great Italian scientist also
made an equally important contribution to the eventual acceptance of
Copernicus' theory. If the heliocentric model were true, then the
whole of physics, essentially unchanged since Aristotle, was in error.
Galileo provided an alternate explanation for motion that did not
require the philosophical conclusions concerning the primacy of Earth
and its place in the center of the universe. In Aristotle's
conception of motion, Earth must be at the center because it did not
move. Motion, or lack of motion, was an inherent characteristic of a
body, and Earth's lack of movement made it different from the
continuously moving heavenly bodies. Galileo, on the other hand, argued
that motion was only an external process and not an inherent
characteristic of the body itself. Movement was not anymore an innate
characteristic of the planets than lack of motion was innately inherent
in Earth. Before the theory that Earth moved could be accepted, these
important consequences regarding the nature of motion had to be
explained.

Galileo also argued that a body in motion would continue in motion
without the continuous influence of an outside force. In fact, it
required an outside force to stop the body's motion. This is the
concept that modern scientists call inertia. This conception of motion
helped to answer one of the claims against Earth's diurnal, or
daily, motion. Opponents of the heliocentric model claimed if Earth spun
on its axis, a ball dropped from a tower would land some distance away
from the base of the tower because Earth had moved beneath it.
Galileo's answer was that the ball already possessed a motion in
the direction of the spinning Earth and would continue with that motion
as it fell, thus landing at the base of the tower.

One disturbing question that arose from Copernicus' theory was
that of stellar parallax. If Earth did revolve about the Sun, the
relative position of the stars should change as Earth moved.
Unfortunately for Copernicans, this stellar parallax could not be
observed. Today we know that stellar parallax can only be observed
through telescopes much more powerful than those available to Galileo
and his contemporaries. In fact, proof of stellar parallax was not
supplied until the work of Friedrich Wilhelm Bessel in the nineteenth
century. Bessel's work provided a final proof for the yearly
motion of Earth revolving around the Sun.

It was also in the nineteenth century that a final proof of the rotation
of Earth on its axis

Aristotle
(
Aristotle, lithograph
.

The Bettmann Archive.

Reproduced by permission
.)

was supplied by the French physicist Jean-Bernard-Léon Foucault.
Foucault suspended a large iron ball from a wire swinging freely from a
height of over 200 feet. As the ball, known as "Foucault's
pendulum," swung in the same vertical plane, Earth rotated
beneath it. Foucault's pendulum is now a common exhibit at many
modern science museums. A series of blocks standing in a circle around
the pendulum are knocked over one by one as Earth rotates once in a
twenty-four hour period.

Bessel's discovery of stellar parallax and Foucault's
pendulum represented the final direct proofs of the two primary motions
of Earth. These nineteenth-century events marked the end of a long
process of discovery begun by Copernicus some four centuries earlier.

User Contributions:

Thank you very much for this page.
I have a project in World History that pertains to this, and the well-written information here has really given me more insight than I needed. This helps a whole lot! (:

Could you please comment on the scientific experiments ( I believe there have been 3 or 4 at least ) that cannot scientifically prove that the earth is moving. Obviously this is foundational to a Heliocentric point of view. I'm curious because I only recently became aware of this important, so called, fact. I'm not a Geocentrist, just a neophyte in astronomy looking for some factual answers.

I am surprised to know that foundation of heliocentric model is not based on strong scientific facts. The arguments given are very wage and rather confusing. Could you please give some scientific facts and experiments to make it more conveyancing. Thanks

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